This invention relates to electric motors, and more particularly to an electric motor having an armature which is at least structurally encased within a thermally conductive plastic, and wherein a fan is integrally formed from a portion of the thermally conductive plastic at one end of the armature.
Electric motors are used in a wide variety of applications involving power tools such as drills, saws, sanding and grinding devices, yard tools such as edgers and trimmers, just to name a few such tools. These devices all make use of electric motors having an armature and a stator. The armature is typically formed from a lamination stack around which a plurality of windings of magnet wires are wound. The magnet wires are coupled at their ends to tangs on a commutator disposed on an armature shaft extending coaxially through the lamination stack. The ends of the magnet wires are secured to the commutator.
In the manufacturing process for the armature described above, once the magnet wires have been secured to the commutator, a xe2x80x9ctricklexe2x80x9d resin is applied over the magnet wires and over the ends of the magnet wires where they attached to tangs associated with the commutator. The process of applying the trickle resin is a somewhat difficult process to manage to obtain consistent results. It also has a number of drawbacks, not the least of which is the cost and difficulty of performing it with reliable, consistent results.
Initially, the trickle process requires the use of a relatively large and expensive oven to carefully preheat the partially assembled armatures to relatively precise temperatures before the trickle resin can be applied. The temperature of the trickle resin also needs to be carefully controlled to achieve satisfactory flow of the resin through the slots in the lamination stack of the armature. It has proven to be extremely difficult to achieve consistent, complete flow of the trickle resin through the slots in the lamination stack. As such, it is difficult to achieve good flow inbetween the magnet wires with the trickle resin to satisfactorily insulate the magnetic wires from one another and hold them stationary relative to each other. A cooling period must then be allowed during which air is typically forced over the armatures to cool them before the next manufacturing step is taken. Further complicating the manufacturing process is that the trickle resin typically has a short shelf life, and therefore must be used within a relatively short period of time.
With present day manufacturing techniques, an additional or secondary coating of a higher viscosity trickle resin is often required to protect the armature (and specifically the magnet wires) from abrasive metal particles that are drawn in and over the armature""s fan when the armature is used in connection with various grinders and sanders. This serves to further increase the manufacturing cost and complexity of the armature.
Still another drawback with the trickle process is the relatively high number of armatures which are often rejected because of problems encountered during the process of applying the trickle resin to an otherwise properly constructed armature. Such problems can include contamination of the commutator of the armature by the trickle resin during the application process, as well as uneven flow of the trickle resin if the pump supplying the resin becomes momentarily clogged. Accordingly, the difficulty in controlling the trickle resin application process produces a relatively large scrap rate which further adds to the manufacturing cost of electric motors.
Still another disadvantage with present day electric motors is that the fan which is typically attached at one end of the armature is a separately formed component which must be glued or otherwise secured to the armature in a separate manufacturing step. This fan also is typically the first component to fail if the motor is stressed. This occurs when the fan simply melts due to overheating of the motor. The use of a separately formed component also takes up additional space on the armature which increases the overall size of the armature.
In view of the foregoing, it would be highly desirable to eliminate the steps of applying the trickle resin and securing a separately formed fan to an armature. More specifically, it would be highly desirable if these two steps could be replaced by a single step which achieves the object of more thoroughly coating the magnet wires of the armature with a thermally conductive material, in addition to forming an integrally formed fan, all with a single manufacturing step.
The present invention is directed to an armature for an electric motor which includes a thermally conductive coating applied over the magnet wires wound around the lamination stack thereof, to thereby form an excellent means for dissipating heat and holding the magnet wires stationary as well as holding the ends of the magnet wires secured to tangs on the commutator. It is also a principal object of the present invention to provide a fan which is integrally molded at one end of the armature from the thermally conductive plastic in a single manufacturing step. The integrally molded fan better resists the extreme temperatures that may be encountered if the motor is stressed during use.
In one preferred embodiment the thermally conductive plastic is applied by a well known injection molding process. As such, the need for a trickle oven and the difficult to manage application of the trickle resin is completed eliminated.
The integrally formed fan is formed when the armature is placed into a suitable molding tool during the injection molding process. The resulting injection molded fan is much more resistant to high temperatures that may be encountered during use of the armature with which it is associated, and further requires less space than previously formed, independent fan components. The smaller fan allows the overall dimensions of the armature to be reduced thereby allowing a smaller motor to be formed for a given ampere rating. Forming the fan integrally with the thermally conductive plastic which coats the magnet wires also eliminates the need to insert portions of the fan into the slots in the lamination stack. This allows more room within the slots in the lamination stack for the magnet wires which allows the power rating of the motor to be increased beyond what would normally be attainable with a conventionally attached and independently formed fan component.
The armature of the present invention thus significantly reduces the complexity and cost of the manufacturing process by completely eliminating the steps involving the application of trickle resin and the attachment of a separately formed fan component, which are two of the most expensive and cumbersome manufacturing steps formed with present day electric motors.